The Cricklewood Greats is about as good as it ever gets. Capaldi and his team understand the grammar of the kind of reverential, fan-based documentary they've decided to take apart. They keep their faces straight, they stay in character. There are flaws, of course. The focus wobbles a bit. The British film industry never had a Melies or a Charlie Chaplin and it was a mis-step to include them in a mickey-take of British film (even though the pastiches are beautifully done). With Jonny Puff they seem to be trying to get at The Archers and Grierson all in one go- and the two are oil and water. But the slaps at Gracie Fields, Peter Cushing and Kenneth Williams are accurate and sufficiently cruel- and there's a delightful sequence in which Terry Gilliam enthusiastically rubbishes himself.
Successful parody comes out of affection, but needs to be merciless- else it would turn to mush. It doesn't kill the thing it loves. It shows us how tawdry and absurd it is, but goes on loving it anyway.